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Bender J.,TU Darmstadt | Muller M.,Nvidia | Otaduy M.A.,URJC Madrid | Teschner M.,Albert Ludwigs University of Freiburg | Macklin M.,Nvidia
Computer Graphics Forum | Year: 2014

The dynamic simulation of mechanical effects has a long history in computer graphics. The classical methods in this field discretize Newton's second law in a variety of Lagrangian or Eulerian ways, and formulate forces appropriate for each mechanical effect: joints for rigid bodies; stretching, shearing or bending for deformable bodies and pressure, or viscosity for fluids, to mention just a few. In the last years, the class of position-based methods has become popular in the graphics community. These kinds of methods are fast, stable and controllable which make them well-suited for use in interactive environments. Position-based methods are not as accurate as force-based methods in general but they provide visual plausibility. Therefore, the main application areas of these approaches are virtual reality, computer games and special effects in movies. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation. We will introduce the concept of position-based dynamics, present dynamic simulation based on shape matching and discuss data-driven upsampling approaches. Furthermore, we will present several applications for these methods. The dynamic simulation of mechanical effects has a long history in computer graphics. The classical methods in this field discretize Newton's second law in a variety of Lagrangian or Eulerian ways, and formulate forces appropriate for each mechanical effect: joints for rigid bodies; stretching, shearing, or bending for deformable bodies; and pressure, or viscosity for fluids, to mention just a few. In the last years the class of position-based methods has become popular in the graphics community. These kinds of methods are fast, stable and controllable which make them well-suited for use in interactive environments. Position-based methods are not as accurate as force-based methods in general but they provide visual plausibility. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation. This state-of-the-art report covers the large variety of position-based methods that were developed in the field of physically based simulation. © 2014 The Authors Computer Graphics Forum © 2014 The Eurographics Association and John Wiley & Sons Ltd.


Bickel B.,Disney Research Zurich | Bacher M.,Harvard University | Otaduy M.A.,URJC Madrid | Lee H.R.,Harvard University | And 4 more authors.
ACM Transactions on Graphics | Year: 2010

This paper introduces a data-driven process for designing and fabricating materials with desired deformation behavior. Our process starts with measuring deformation properties of base materials. For each base material we acquire a set of example deformations, and we represent the material as a non-linear stress-strain relationship in a finite-element model. We have validated our material measurement process by comparing simulations of arbitrary stacks of base materials with measured deformations of fabricated material stacks. After material measurement, our process continues with designing stacked layers of base materials. We introduce an optimization process that finds the best combination of stacked layers that meets a user's criteria specified by example deformations. Our algorithm employs a number of strategies to prune poor solutions from the combinatorial search space. We demonstrate the complete process by designing and fabricating objects with complex heterogeneous materials using modern multi-material 3D printers. © 2010 ACM.


Tang M.,Zhejiang University | Manochay D.,University of North Carolina at Chapel Hill | Otaduyz M.A.,URJC Madrid | Tongx R.,Zhejiang University
ACM Transactions on Graphics | Year: 2012

We present a simple algorithm to compute continuous penalty forces to determine collision response between rigid and deformable models bounded by triangle meshes. Our algorithm computes a well-behaved solution in contrast to the traditional stability and robustness problems of penalty methods, induced by force discontinuities. We trace contact features along their deforming trajectories and accumulate penalty forces along the penetration time intervals between the overlapping feature pairs. Moreover, we present a closed-form expression to compute the continuous and smooth collision response. Our method has very small additional overhead compared to previous penalty methods, and can significantly improve the stability and robustness. We highlight its benefits on several benchmarks. © 2012 ACM 0730-0301/2012/08-ART107.


Schvartzman S.C.,URJC Madrid | Perez A.G.,URJC Madrid | Otaduy M.A.,URJC Madrid
ACM Transactions on Graphics | Year: 2010

Collision detection is a problem that has often been addressed efficiently with the use of hierarchical culling data structures. In the subproblem of self-collision detection for triangle meshes, however, such hierarchical data structures lose much of their power, because triangles adjacent to each other cannot be distinguished from actually colliding ones unless individually tested. Shape regularity of surface patches, described in terms of orientation and contour conditions, was proposed long ago as a culling criterion for hierarchical self-collision detection. However, to date, algorithms based on shape regularity had to trade conservativeness for efficiency, because there was no known algorithm for efficiently performing 2D contour self-intersection tests. In this paper, we introduce a star-contour criterion that is amenable to hierarchical computations. Together with a thorough analysis of the tree traversal process in hierarchical self-collision detection, it has led us to novel hierarchical data structures and algorithms for efficient yet conservative self-collision detection. We demonstrate the application of our algorithm to several example animations, and we show that it consistently outperforms other approaches. © 2010 ACM.


Alduan I.,URJC Madrid | Otaduy M.A.,URJC Madrid
Proceedings - SCA 2011: ACM SIGGRAPH / Eurographics Symposium on Computer Animation | Year: 2011

Combining mechanical properties of solids and fluids, granular materials pose important challenges for the design of algorithms for realistic animation. In this paper, we present a simulation algorithm based on smoothed particle hydrodynamics (SPH) that succeeds in modeling important features of the behavior of granular materials. These features are unilateral incompressibility, friction and cohesion. We extend an existing unilateral incompressibility formulation to be added at almost no effort to an existing SPH-based algorithm for fluids. The main advantages of this extension are the ease of implementation, the lack of grid artifacts, and the simple two-way coupling with other objects. Our friction and cohesion models can also be incorporated in a seamless manner in the overall SPH simulation algorithm. Copyright © 2011 by the Association for Computing Machinery, Inc.


Schvartzman S.C.,Stanford University | Otaduy M.A.,URJC Madrid
Proceedings of the Symposium on Interactive 3D Graphics | Year: 2014

We propose a novel algorithm to simulate brittle fracture. It augments previous methods based on Voronoi diagrams, improving their versatility and their ability to adapt fracture patterns automatically to diverse collision scenarios and object properties. We cast brittle fracture as the computation of a high-dimensional Centroidal Voronoi Diagram (CVD), where the distribution of fracture fragments is guided by the deformation field of the fractured object. By formulating the problem in high dimensions, we support robustly object and crack concavities, as well as intuitive artist control. We further accelerate the fracture animation process with example-based learning of the fracture degree, and a highly parllel tessellation algorithm. As a result, we obtain fast animations of detailed and rich fractures, with fracture patterns that adapt to each particular collision scenario. Copyright © ACM.


Cirio G.,URJC Madrid | Lopez-Moreno J.,URJC Madrid | Otaduy M.A.,URJC Madrid
Proceedings - SCA 2015: 14th ACM SIGGRAPH / Eurographics Symposium on Computer Animation | Year: 2015

Knitted cloth is made of yarns that are stitched in regular patterns, and its macroscopic behavior is dictated by the contact interactions between such yarns. We propose an efficient representation of knitted cloth at the yarn level that treats yarn-yarn contacts as persistent, thereby avoiding expensive contact handling altogether. We introduce a compact representation of yarn geometry and kinematics, capturing the essential deformation modes of yarn loops and stitches with a minimum cost. Based on this representation, we design force models that reproduce the characteristic macroscopic behavior of knitted fabrics. We demonstrate the efficiency of our method on simulations with millions of degrees of freedom (hundreds of thousands of yarn loops), almost one order of magnitude faster than previous techniques. © 2015 ACM.


Gascon J.,URJC Madrid | Espadero J.M.,URJC Madrid | Perez A.G.,URJC Madrid | Torres R.,URJC Madrid | Otaduy M.A.,URJC Madrid
Proceedings - SCA 2013: 12th ACM SIGGRAPH / Eurographics Symposium on Computer Animation | Year: 2013

Many inherently deformable structures, such as human anatomy, are often represented using a regular volumetric discretization, e.g., in medical imaging. While deformation algorithms employ discretizations that deform themselves along with the material, visualization algorithms are optimized for regular undeformed discretizations. In this paper, we propose a method to transform highresolution volume data embedded in a deformable tetrahedral mesh. We cast volume deformation as a problem of tetrahedral rasterization with 3D texture mapping. Then, the core of our solution to volume data deformation is a very fast algorithm for tetrahedral rasterization. We perform rasterization as a massively parallel operation on target voxels, and we minimize the number of voxels to be handled using a multi-resolution culling approach. Our method allows the deformation of volume data with over 20 million voxels at interactive rates.


Teng Y.,University of California at Santa Barbara | Otaduy M.A.,URJC Madrid | Kim T.,University of California at Santa Barbara
ACM Transactions on Graphics | Year: 2014

We present an efficient new subspace method for simulating the self-contact of articulated deformable bodies, such as characters. Self-contact is highly structured in this setting, as the limited space of possible articulations produces a predictable set of coherent collisions. Subspace methods can leverage this coherence, and have been used in the past to accelerate the collision detection stage of contact simulation. We show that these methods can be used to accelerate the entire contact computation, and allow self-contact to be resolved without looking at all of the contact points. Our analysis of the problem yields a broader insight into the types of non-linearities that subspace methods can efficiently approximate, and leads us to design a pose-space cubature scheme. Our algorithm accelerates self-contact by up to an order of magnitude over other subspace simulations, and accelerates the overall simulation by two orders of magnitude over full-rank simulations. We demonstrate the simulation of high resolution (100K - 400K elements) meshes in self-contact at interactive rates (5.8 - 50 FPS). Copyright © ACM.


Miguel E.,URJC Madrid | Miraut D.,URJC Madrid | Otaduy M.A.,URJC Madrid
Computer Graphics Forum | Year: 2016

In this paper, we present a method to model hyperelasticity that is well suited for representing the nonlinearity of real-world objects, as well as for estimating it from deformation examples. Previous approaches suffer several limitations, such as lack of integrability of elastic forces, failure to enforce energy convexity, lack of robustness of parameter estimation, or difficulty to model cross-modal effects. Our method avoids these problems by relying on a general energy-based definition of elastic properties. The accuracy of the resulting elastic model is maximized by defining an additive model of separable energy terms, which allow progressive parameter estimation. In addition, our method supports efficient modeling of extreme nonlinearities thanks to energy-limiting constraints. We combine our energy-based model with an optimization method to estimate model parameters from force-deformation examples, and we show successful modeling of diverse deformable objects, including cloth, human finger skin, and internal human anatomy in a medical imaging application. © 2016 The Author(s) Computer Graphics Forum © 2016 The Eurographics Association and John Wiley & Sons Ltd. Published by John Wiley & Sons Ltd.

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